The present invention relates generally to automatic frequency control circuits, frequency detection circuits, and the like. Specifically, the present invention relates to an extremely accurate frequency resolution circuit that achieves a locked condition within a short time interval. More specifically, the present invention relates to a frequency resolution circuit which tolerates both amplitude and pulse modulation of the signal whose frequency it resolves.
A great many electronic applications encode information into an AC signal in order to transmit the information. Many forms of encoding are known, such as amplitude modulation, frequency modulation, and pulse modulation. In order to recover the encoded information, a device which receives the AC signal must decode the information from the AC signal.
The present invention decodes frequency modulation information of such signals by providing solutions to three problems. First, the present invention achieves an extremely accurate resolution of the frequency of the encoded signal. For example, the present invention has demonstrated a frequency resolution accuracy of 1 part in 100,000,000. Second, the present invention achieves this frequency resolution in a reasonably fast time interval. For example, a locking time of 0.01 second has been demonstrated by the present invention. And third, the present invention achieves the frequency resolution regardless of whether the encoded signal is further modulated with pulse and amplitude information.
Phase locked loop circuits are well known in the art and have been used in various frequency control and frequency resolution circuits. However, such circuits fail to achieve the performance of the present invention.
Accordingly, it is one object of the present invention to provide an apparatus which resolves the frequency of an incoming signal to an extreme level of accuracy.
Another object of the present invention concerns providing an apparatus that achieves a locked condition in a relatively short time interval. The locked condition occurs when the unknown frequency of the input signal is resolved within some predetermined level of accuracy.
Still another object of the present invention relates to having frequency resolution circuitry which demonstrates a high level of performance even in the presence of signals which may be both amplitude and pulse modulated in addition to being frequency modulated.
Yet another object of the present invention relates to providing a reasonably stable, noise tolerant system.